Digital computer systems are used in a number of applications in which virtually continuous availability of data is important to the operation of businesses or other entities using the systems. Generally, computer centers will periodically produce back-up copies of data on their various digital computer systems. Such back-up copies are usually not maintained on a continuous basis, but instead at particular points in time, often at night, and in any case represent the data at the particular points in time at which the back-up copies are generated. Accordingly, if a failure occurs between back-ups, data which has been received and processed by the digital computer systems since the last back-up copy was produced, may be lost.
Typically, such back-up copies will be maintained by the computer centers at their respective sites so that they may be used in the event of a failure, although some off-site archival back-ups may be maintained. Significant additional problems arise in the case of, for example, catastrophic events that can occur, such as may result from, for example, fire, flood or other natural disasters, intentional tampering or sabotage and the like, which may result in unintentional or intentional damage to an entire site or some significant portion thereof, since some or all of the back-up copies may also be damaged and the data contained thereon may be unavailable.
The invention provides a new and improved digital data storage subsystem which provides secure remote mirrored storage of digital data for one or more digital data processing systems.
In brief summary, the invention provides a data item reconstruction element for, during a reconstruction operation, reconstructing information stored on a back-up information storage subsystem associated with at least one protected volume. The back-up information storage subsystem includes a plurality of storage media each associated with one of a plurality of sets, the information associated with the protected volume being stored on storage media associated with one of the sets. The data item reconstruction element during the reconstruction operation retrieves in parallel information from a plurality of the storage media associated with the one of the sets on which information associated with the at least one protected volume is stored, to obtain the information which is associated with the protected volume.
In one particular embodiment, the storage media comprise magnetic tape cassettes. Since all of the data associated with a particular protected volume is stored on one of the sets, only the tape cassettes of the set on which the protected volume is stored needs to be used in the reconstruction operation, instead of all of the cassettes in the back-up information storage subsystem. This serves to reduce the amount of time required to perform the reconstruction operation for the protected volume.